Findings in the medical field have documented the importance of light in the stability of a person's energy, mood, sleep, concentration, and in the regulation of the person's circadian rhythms. Light deprivation has been shown to cause what is generally known as winter depression or Seasonal Affective Disorder, which is manifested by symptoms including fatigue, irritability, anxiety, weight gain, social withdrawal, and a lack of alertness. This condition affects from five to twenty percent of the population, with prevalence rates being the greatest in high latitude regions of the world. In the northern hemisphere, people suffering from Seasonal Affective Disorder generally experience a decline in mood around October that usually resolves by April. Other commonly affected people include those living in frequently overcast areas and night-shift workers.
As with many biopsychiatric disorders, Seasonal Affective Disorder is theorized to be related to neurotransmitter levels in the brain. For example, serotonin and serotonin pathways have been implicated in depressive disorders. The production of melatonin, which is a metabolite of serotonin and is synthesized in the pinealcytes, is apparently influenced solely by the light-dark cycle. In most animals, melatonin production begins in the evening, during which time melatonin levels abruptly rise in concentration. The melatonin levels peak during the night and then decline to a low, daytime concentration before dawn.
The production of melatonin from the pineal gland is stimulated by sympathetic neuronal output from the suprachiasmatic nuclei. This appears to function as an internal pacemaker or body clock located in the hypothalamus. The body clock is regulated by the light-dark cycle as sensed by the visual system. Photic input transmitted by the retinohypothalamic tract synchronizes the suprachiamatic nuclei to the light-dark cycle.
Increasing evidence points towards the non-dominant hemisphere of the brain as the primary site where mood is regulated, with a lesser contribution from the dominant hemisphere. In fact, a host of psychiatric disorders such as depressive disorders, anxiety disorders, affective disorders, sleep disorders, impulse control disorders, eating disorders, addictive disorders, obsessive disorders, impulse control disorders and learning disorders may be due to an imbalance of functioning between the non-dominant and the dominant cerebral hemispheres.
Light therapy has been successfully used to treat patients afflicted with Seasonal Affective Disorder. Light therapy typically involves the exposure of such patients to approximately one hour of light either in the morning or evening depending on the manifestations of their affliction. Commercially available lamps or light boxes generally provide from 2,500 to 10,000 lux illumination in an attempt to simulate summer light levels. Most light boxes include panels of light bulbs covered with a sheet of plexiglass that diffuses the light and a parabolic reflector to focus the light in the direction of the patient. Examples of apparatuses for providing light therapy are disclosed in the following United States patents: U.S. Pat. No. 5,343,121 to Terman, et al.; U.S. Pat. No. 5,292,345 to Gerardo; U.S. Pat. No. 5,149,184 to Hughes, et al.; and U.S. Pat. No. 5,047,006 to Brandston, et al.
Dr. Marcelo Enrique Lopez-Claros, postulates that light therapy directed predominantly or exclusively to the non-dominant cerebral hemisphere will lead to photic stimulation and thereby metabolic stimulation primarily in the non-dominant cerebral hemisphere, ultimately resulting in the correction of the imbalances present in the aforementioned disorders. Currently available light therapy devices, including the aforementioned patented apparatuses, are incapable of selectively stimulating the nondominant hemisphere. Rather, currently available light therapy devices stimulate both cerebral hemispheres essentially equally.